In manufacturing semiconductor devices, resist patterns have been required to be made minute enough to meet increased integration density and highly accelerated processing speed in LSIs. Resist patterns are normally formed in photo-lithographic processes from, for example, positive-working type resists, whose solubilities to alkaline developers are increased by exposure to light. Accordingly, the resists in the areas exposed to light are removed away with the alkaline developers to form positive resist patterns. However, the fineness of the resultant patterns greatly depends on the exposure methods and light sources, and hence in order to stably produce fine resist patterns, a huge investment is necessary to install special and expensive facilities and equipments needed for the exposure methods and light sources capable of ensuring the fineness.
In view of that, there are various techniques studied for further miniaturizing resist patterns formed beforehand by conventional methods. For example, they include a practical method in which a resist pattern stably produced by a conventional method is coated with a composition comprising a water-soluble resin and optional additives so as to fatten or thicken the resist pattern and thereby to decrease the diameter of holes and/or the width of furrow lines separating the ridges in the pattern.
Specifically, the following processes and composition are known:
(1) a process comprising the steps of
coating a conventionally formed resist pattern with a composition crosslinkable by an acid,
heating the resist pattern to diffuse the acid comprised in the resist so that the composition on the resist may be crosslinked to form a crosslinked layer at the interface therebetween as a covering layer of the resist pattern, and
removing the uncrosslinked composition with a developer to fatten or thicken the resist pattern and thereby to decrease the diameter of holes and/or the width of furrow lines separating the ridges in the pattern (see, Patent documents 1 and 2);
(2) a process comprising the steps of
coating a conventionally formed resist pattern with an aqueous solution of a copolymer derived from (meth)acrylic acid monomers and water-soluble vinyl monomers, and
heating the resist pattern to shrink and thereby to become finer (see, Patent document 3); and
(3) a water-soluble coating composition which comprises a polymer comprising amino groups, in particular, primary amines and which is used for covering a photoresist pattern (see, Patent document 4).
However, when the pattern to be miniaturized is intended to be formed before the above miniaturization process, it is difficult to stably obtain a pattern near the resolution limit. In order to improve this problem, studies have been made on methods for stably forming patterns near the resolution limit by use of organic solvent developers. For example, there is a known method in which line width variance (LWR), exposure latitude (EL) and depth of focus (DOF) are improved enough to form stably a pattern by combination of a positive-working type resist composition and an organic solvent developer (see, Patent document 5). In this method, the resist in the exposed area becomes highly soluble in an alkaline developer but hardly soluble in an organic solvent. By making use of that, the method makes it possible to form a negative pattern from a positive-working type resist.
Further, after thus formed from a positive-working type resist, the negative pattern can be further improved in resolution by a technique in which a composition comprising a crosslinking agent is cast on the pattern and then heated and rinsed away (see, Patent document 6).